Seasonal sow infertility: Insulin's possible role studied

IOWA State University animal scientists are searching for reasons and solutions for seasonal infertility in sows, including what may be the first scientific study of insulin's possible role in the problem.

Iowa State assistant professors of animal science Aileen Keating and Jason Ross estimate that seasonal infertility costs Iowa pork producers about $60 million a year, and nationally, the losses to the swine industry are approximately $420 million annually.

"After a long, hot summer, pigs have problems with either getting pregnant or maintaining a pregnancy," Keating said.

Other Iowa State scientists are studying heat stress in pigs, and exposure to that study plus Keating's knowledge of reproductive physiology and ovarian dysfunction are what triggered her interest in studying the role of insulin.

Noting that the sows in the heat stress study had high levels of insulin, Keating said high circulating insulin levels and problems with infertility and maintaining a pregnancy are common among obese women.

"When women are obese, they have problems with fertility," Keating said. "Obese women don't ovulate very well, and even when they are medically induced to ovulate, their eggs are not very good quality. In women, obesity is associated with high circulating insulin levels."

When pigs are heat-stressed, they don't eat much, but even though they aren't eating, heat stress causes elevations in circulating insulin, Keating said.

"That's the opposite of normal in any animal," she said. "Normally, when animals eat, (they) have a high level of blood glucose, and then insulin is released to get blood glucose levels back to normal. So, usually, insulin goes up after you've eaten, but these heat-stressed animals have suppressed feed intake."

Keating said she was interested in exploring what she called a "weird physiological phenomenon" because seasonal infertility has such a large economic cost to swine producers.

She believes her team may be the first to study a potential insulin link to seasonal infertility in swine.

A $53,000 grant from the Iowa Pork Producers Assn. is allowing Keating and Ross to conduct research on the ovaries of the pigs in Iowa State's heat stress studies.

Early findings indicate that there may be changes to the pathway that makes estrogen in the ovary of a heat-stressed pig, which could play a role in seasonal infertility.

"If you don't have an estrogen release, you don't have ovulation. In pigs, it's also what's needed for them to display that they are in heat and to be inseminated," Keating said. "Estrogen is also necessary for maternal recognition of pregnancy. So, when a pig has a fertilized egg, estrogen is what signals to the pig's body to provide support for growth and not reject the egg as a foreign invader. We want to know more about what's happening with estrogen levels in pigs and the seasonal infertility issue."

Keating is hopeful that they may begin to identify therapies or intervention strategies during the study. Additional research will be needed — including conducting trials — before any recommendations can be made to producers.

"In the future, we would like to be able to do some larger trials employing mitigation strategies that are applicable to Iowa. We would like to be able to identify something that could make a difference and do something that helps the economy. If we can come up with a kind of therapy or intervention strategy, it could save a lot of money for Iowa producers and those around the U.S. and abroad. This is a global problem," she said.

Improving sperm survival

Although U.S. cattle genetics are exported all over the world in the form of frozen semen, the same is not true for swine, because boar semen does not freeze well.

In an attempt to improve semen storage and pig reproduction, animal scientists at the University of Illinois are looking at how sperm survives in the sow oviduct.

"Many mammals and birds will store sperm for some period of time," University of Illinois associate professor of animal sciences David Miller said. "Pigs will store sperm for 24-48 hours."

He added that sperm must be stored in species in which mating and ovulation are poorly synchronized.

Miller and his team wanted to understand the adhesion system that retains the sperm. Previous research indicated that sugars in the oviduct were an important part of the process, but it was not clear which sugars.

They screened hundreds of sugars using an array on a microscope slide to which they added fluorescently labeled boar semen. When the semen was bound to a sugar, fluorescence was visible on the slide. They identified two sugars: sialylated lactosamine and Lewis X.

The next step is to identify the receptor on the sperm.

"We'd like to know exactly to which molecules the sugars bind," Miller said. "Then, maybe we could develop a laboratory test for those molecules. If sperm have a lot of them, then maybe it would be possible to inseminate only once rather than two or three times, as is typical when inseminating sows."

He noted that a better understanding of the storage process might also help the team determine what goes wrong when sperm are less fertile. If the problem is linked to the storage process, it might be possible to develop therapies to correct it.

Another question to explore is how the sugars lengthen the life span of sperm. If this could be determined, it might be possible to extend the amount of time semen can be stored, making it easier to ship it to other places.

"If we can improve storage and transportation, we can affect pig genetics worldwide, not just within our region," he said.

The research was described in "Porcine Sperm Bind to Specific 6-Sialylated Biantennary Glycans to Form the Oviduct Reservoir" by G. Kadirvel, S.A. Machado, C. Korneli, E. Collins, P. Miller, K.N. Bess, K. Aoki, M. Tiemeyer, N. Bovin and D.J. Miller, which was recently published in Biology of Reproduction.

Mineral concentrations

Following the drought of 2012, the prices of corn and soybean meal for livestock diets increased significantly, so in an effort to reduce feed costs, pork producers have looked for alternative sources of calcium and phosphorus.

University of Illinois researchers have developed equations for calculating the concentrations of these minerals in byproducts from the rendering industry.

Professor of animal sciences Hans H. Stein and his team determined the digestibility of calcium and phosphorus in meat and bone meal (MBM), which is commonly used as a source of protein in animal diets. MBM contains greater concentrations of calcium and phosphorus than all plant feed ingredients, so it can replace inorganic phosphates in swine diets without harming the bones or negatively affecting the growth of the animals.

However, to use MBM effectively as a source of phosphorus and calcium, producers need an accurate assessment of the digestibility of these minerals when fed to pigs.

"There is quite a bit of variability in meat and bone meal, which is probably caused by different types of raw materials going into it," Stein said.

The researchers formulated eight diets using MBM from five companies in the U.S. The ninth diet was phosphorus free and was used to determine the endogenous losses of phosphorus from the animals. This value was used to calculate the standardized total tract digestibility of phosphorus in the eight sources of MBM.

Results indicated that there is a negative correlation between the ash content in MBM and the digestibility of calcium and phosphorus, but all sources of MBM had a relatively high digestibility of calcium and phosphorus, an announcement said. Moreover, calcium and phosphorus concentrations varied from two to four times more among the batches of MBM than protein and acid-hydrolyzed ether extract concentrations. However, ash content had a highly significant positive correlation with calcium and phosphorus concentrations.

"Thus, if you know the concentration of ash, you can calculate the concentration of calcium and phosphorus," Stein said. "Ash is easy and inexpensive to analyze."

Stein and his team also developed equations to calculate calcium and phosphorus concentrations in MBM and proposed models for estimating the standardized total tract digestibility of phosphorus and apparent total tract digestibility of calcium.

The equations and the research appeared in "Digestibility of Phosphorus & Calcium in Meat & Bone Meal Fed to Growing Pigs" by R.C. Sulabo and H.H. Stein, which was recently published in the Journal of Animal Science.